Conventionally, in a vehicle such as a motor vehicle or the like, so many opening and closing members are provided, such as a door, a sunroof, a backdoor and the like, the members being attached to a vehicle so as to be freely opened and closed. In particular, in a station wagon vehicle, a minivan vehicle and the like, there are frequently seen a structure in which a backdoor is provided in a rear end portion of the vehicle so as to make it easy to load and unload a baggage from a rear portion of the vehicle. Normally, the backdoor mentioned above is attached to the vehicle via a hinge fixed to a rear end portion of a vehicle roof by setting a rotational supporting point to be horizontal, and is structured such as to open and close in a vertical direction around the rotational supporting point of the hinge. In this case, since the backdoor is largely flipped up above the vehicle, it is also called as a lift gate, a rear hatch or the like.
However, since it is often the case that the backdoor mentioned above is large-scaled and heavy, there is a case that it is hard to easily open and close the backdoor particularly by a woman or a child. In particular, since the backdoor is largely flipped upward at a time when it becomes in a fully open state, it is further hard to open and close the backdoor.
Accordingly, under a condition that a family use of the minivan vehicle or the like is increased, there appears a vehicle in which an automatic opening and closing apparatus for the backdoor is mounted for the purpose of easily opening and closing the backdoor even by the woman or the child, and it tends to be increased. Further, since it is possible to remote operate the backdoor by placing the automatic opening and closing apparatus even when it is beyond a hand of an operator in a driver's seat, it is considerable to required to mount the automatic opening and closing apparatus in view of this convenience.
In the automatic opening and closing apparatus of the backdoor mentioned above, a connection rod is generally connected to a position a predetermined distance apart from the rotational supporting point of the hinge in the backdoor, and the structure is made such that the backdoor is opened and closed by driving the connection rod by means of an actuator. As the actuator of the type mentioned above, there is a structure provided with a slide mechanism having an annular rectangular channel fixed to the vehicle and a rack bar arranged so as to freely move in an axial direction within the channel, and opening and closing the backdoor by integrally oscillating another end of the connection rod with the rack bar in a linear manner, for example, as shown in Japanese Patent Application Laid-Open No. 2001-253241 (the corresponding U.S. patent application Ser. No. 09/756,416 filed on Jan. 8, 2001: patent application Publication No. US 2001/0047625 A1 published on Dec. 6, 2001). In this case, the actuators are arranged within pillars in both sides of the vehicle in a rear end portion of the vehicle by setting an axial direction of the slide mechanism to be substantially vertical. Rack gears arranged lining up in the axial direction over against a window portion formed in a side wall of the channel are formed in the rack bar, and these rack gears are engaged with pinion gears in the window portion of the channel. The pinion gear is structured such as to be rotated and driven by a power unit having an electric motor corresponding to a drive source, and the electric motor is operated, whereby the structure is made such that the rack bar is linearly oscillated along the channel. Further, a ball stud is fixed to a surface opposite to the rack gear of the rack bar, and the ball stud protrudes to an external portion via a slot extending in the axial direction which is formed in the side wall of the channel so as to be connected to another end of the connection rod. Further, when the electric motor is operated, a linear oscillating motion of the rack bar is converted into the opening and closing operation of the backdoor via the connection rod, whereby the backdoor is automatically opened and closed.